Calling all 603 owners,and gurus .
So like the title says,does anybody knows what is the "normal" coolant pressure for OM603 (mine is 603.971)?I search the web and Mercedes manual but I can not find the information .
I have no problems,no overheating,no coolant loss,nothing except that to me hoses feel little hard,not rock hard but still harder than I think they should be.I can squeeze them maybe 1/3-1/4.
And after night I still have a small amount of pressure in the system,the hoses are soft,but when I open the cap I hear a whoosh sound .
So any info would be appreciated.

Oh and i forgot to mention,that my brother did a full head job(he had coolant in cylinders),before I bought the car from him,maybe 30000 miles ago.
And I also noticed that the lower hose is cool,I changed the T-stat when i bought the car out of precaucion.And last week I tested it and it opens normal,but i drilled a 6mm hole just in case.Once again the temp is normal 80-90 C,no coolant loss,no coolant smell,no white smoke from the exhaust,nothing unusual except the pressure .

Thanks in advance.

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Mercedes W140, S350TD, 95.
Mercedes W140, S350, 92.
Porsche 944, 86 N/A.
Porsche 944, 85 N/A automatic.
Porsche 944, 84 N/A.
Porsche 944, 83 N/A.
Opel GT, 73.
Toyota Supra MA61,84.

Air pockets? Bad radiator cap? I'd probably be hoping it's something like that.

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1983 W123 300TD US spec Turbo engine, with Euro bumpers and manual climate control, and manual transmission.

There is no such thing as 'normal' pressure. The vent cap, depends on rating, will release the pressure to the overflow tank. So it will be never go over the cap rating. There is member who wants to measure the 'pressure' but I think it is a futile exercise.

If it feels soft overnight then do not worry about it. Have a beer and relax.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

I cleaned the radiator inside and outside,no air pockets 99% sure,I have bought a new rad cap still no change.Pressure is still present.I will check for bubbles in the coolant tomorrow.
I drove the car up until recently with bad rad cap,that held no pressure,then when i bought a new rad cap I noticed the pressure in the system so i don't know what is "normal" pressure on this TD engines.

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Mercedes W140, S350TD, 95.
Mercedes W140, S350, 92.
Porsche 944, 86 N/A.
Porsche 944, 85 N/A automatic.
Porsche 944, 84 N/A.
Porsche 944, 83 N/A.
Opel GT, 73.
Toyota Supra MA61,84.

Mine does that too. Just get a lower pressure radiator cap from a gasser. Problem solved.

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CENSORED due to not family friendly words

I already took a beer,and I am relaxed,if it brakes down I will fix it,it is just out of curiosity .

__________________
Mercedes W140, S350TD, 95.
Mercedes W140, S350, 92.
Porsche 944, 86 N/A.
Porsche 944, 85 N/A automatic.
Porsche 944, 84 N/A.
Porsche 944, 83 N/A.
Opel GT, 73.
Toyota Supra MA61,84.

I have a 140(1,4bar) cap,put a 120(1,2bar) and still no change,but I am O.K. until i start to loose coolant .

__________________
Mercedes W140, S350TD, 95.
Mercedes W140, S350, 92.
Porsche 944, 86 N/A.
Porsche 944, 85 N/A automatic.
Porsche 944, 84 N/A.
Porsche 944, 83 N/A.
Opel GT, 73.
Toyota Supra MA61,84.

Yup exactly what I did. The important bit is how much pressure do you have in the system the next morning. With 140 cap my upper rad hose was still solid in the morning, with 120 cap its not. Theres no hiss when I open the cap. I know combustion gases are leaking into the cooling system with the #14 head but it seems manageable. It doesn't consume any coolant. I've put 20k miles on it like this so far. I keep telling myself this summer I'll swap in the #17 head that's been sitting in my garage since 2012. This summer I'll do it... for sure... scouts honor

Theres a lot you can do to mitigate any cooling issues like run a colder thermostat (71c in my case), electric cooling fans triggered early (87c), smaller water pump pulley off an M103 (spins the water pump 15% faster) and run 2/3 water.

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CENSORED due to not family friendly words

If you have ANY pressure in the system the next morning, you have a blocked radiator. Period, end of story, no other way this could happen. You are headed for trouble, no matter what cap you use.

OP-
I think this is a thread that might be helpful:
http://www.peachparts.com/shopforum/diesel-discussion/350381-w124-coolant-system-pressure-gauge.html#post3277660

Mxfrank-
If your statement is true, then an awful lot of OM603 owners have wasted money replacing cracked heads when they should have replaced their radiator. In other words, yes, there are other ways you could have a pressurized cooling system in the morning.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

I wouldn't be so sure about that. The radiator and hoses were brand new when I bought the car with receipts. Changing the cap from 140 to 120 resolved the cold pressure issue. The cylinder head still leaks combustion gasses into the cooling system but the lower pressure cap keeps the problem in check. I'm sure some car somewhere has a blocked radiator but your categorical conclusion is not true. Hair line cracks in the OM603's #14 head is a well documented problem.

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CENSORED due to not family friendly words

Thanks for the advice,but my car is from 95 and I don't think I have a #14 head,which doesn't rule out that it is cracked or bad gasket .
And I don't have overheating problems,just a pressure problem,and the symptoms are the same with 140 cap and 120 cap,in the morning in both cases hoses were soft but there is a (not big,rather small whoosh) sound when I open tank cap.
And the radiator was cleaned and tested for blockage.But just in case I will try with new T-stat,and another radiator.If that changes nothing,I'll drive it as is and wait for something to happen .

__________________
Mercedes W140, S350TD, 95.
Mercedes W140, S350, 92.
Porsche 944, 86 N/A.
Porsche 944, 85 N/A automatic.
Porsche 944, 84 N/A.
Porsche 944, 83 N/A.
Opel GT, 73.
Toyota Supra MA61,84.

My data (and see the referenced thread) shows that in a 606 engine (603 should be similar) the pressure runs around 10 to 12 psi on a "normal" day of running around town, driving on the freeway, etc. Climbing mountains, etc., very hot weather, etc., pushes the pressure higher, obviously. The highest I've seen is 15-16 psi in the Sierra after a long upgrade on a fairly warm day with a/c running.

It takes several hours for the pressure to drop after parking the car and there's usually a bit of pressure in the system even the next morning.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Thank you all for reply's and info

__________________
Mercedes W140, S350TD, 95.
Mercedes W140, S350, 92.
Porsche 944, 86 N/A.
Porsche 944, 85 N/A automatic.
Porsche 944, 84 N/A.
Porsche 944, 83 N/A.
Opel GT, 73.
Toyota Supra MA61,84.

I suppose the system could be pressurized by exhaust gas, but then you would be able to detect in by testing. Whether the system is pressurized by hot gas or hot fluid, pressure should drop when the engine cools. I suppose I could be wrong, it's been known to happen.